REPORT OF THE CHIEF ASTRONOMER 517 



SESSIONAL PAPER No. 25a 



The question of the thickness of Triassic beds actually exposed in the 

 Boundary belt cannot be fully answered. A safe minimum is 1,000 feet but 

 there is reason to believe that it is much greater. The great monocline of 

 Cultus ridge alone seems to carry between 6,000 and 7,000 feet of beds, chiefly 

 argillite with subordinate sandy layers. The possibility of duplication in this 

 section makes it advisable to place the minimum thickness at no more than 

 half the apparent thickness, say, 3,000 feet. The exposures both in this mono- 

 clinal section and elsewhere are too poor to permit of even an approximate 

 columnar section for the Triassic formation. 



Fossils. — The only fossils found in the Cultus formation were discovered in 

 1906 at a point about 500 yards south of the Boundary and 900 yards west-south- 

 west of Monument 47. Here the. staple black to dark-gray argillite is very 

 homogeneous and carries few lenses of sandstone. Near the bottom of the 800- 

 foot section, where the Boundary Commission trail crosses the creek, the fossils 

 were discovered. Throughout the section the strike averages N. 65° E., and the 

 dip, 45° S.S.E. There is considerable evidence of local slippings, with some 

 brecciation and slickening of the argillite. The fossils are usually much dis- 

 torted; all of them were found in a thin band close to a plane of slipping. 



The writer owes the determination of the fossils, so far as that was possible, 

 to the kindness of Dr. T. W. Stanton, of Washington. He writes: — 



'Lot No. 1502 contains: 



Arniotiftes vancouveremis Whiteaves? Numerous, more or less dis- 

 torted specimens apparently belonging to this species. 



Aulacoceras ? sp. A single fragment of a belemnoid which resembles 

 A. carlottense Whiteaves. 



' The lot numbered 1502, consists almost entirely of ammonites which 

 seem to be identical with some described from the Triassic of Vancouver 

 and Queen Charlotte Islands. Like the original types with which they are 

 compared, they are not well enough preserved to show the septa and other 

 features that are needed for their accurate classification.' 



Combining this paleontological evidence with a comparison of the lithology 

 of the Cultus formation and the Triassic rocks of Vancouver island, the writer 

 has come to the view that little doubt need be entertained as to the Triassic 

 age of the Cultus beds. Neither limestone nor contemporaneous volcanic 

 matter have been found in association with the Cultus argillites, but this 

 failure, by which we recognize an important difference from the Triassic sec- 

 tions of Dawson, can be readily explained on the view that these formations, 

 if present, are faulted out of sight in the Cultus lake region. It is, of couree, 

 possible, though not probable, that these important members bore apparently 

 missing, were never laid down in the Chilliwack region. 



